Fix the name of cpu=aarch64

arm64 is the .deb architecture for it, not the bazel CPU name I see
used.

Change-Id: I46dbbc2478aae92b2a9dba0b8b11a8f54481ef9a
diff --git a/third_party/BUILD b/third_party/BUILD
index 2f22b0e..1ef7169 100644
--- a/third_party/BUILD
+++ b/third_party/BUILD
@@ -121,7 +121,7 @@
     visibility = ["//visibility:public"],
     deps = select({
         "//tools:cpu_k8": ["@lzma_amd64//:lib"],
-        "//tools:cpu_arm64": ["@lzma_arm64//:lib"],
+        "//tools:cpu_aarch64": ["@lzma_arm64//:lib"],
         "//conditions:default": [],
     }),
 )